Copter: CompassMot current calibration

Was using a hardcoded (330) value instead of COMPASS_MAGFIELD_EXPECTED define

ArduCopter/setup.pde

@@ -357,7 +357,7 @@ setup_compassmot(uint8_t argc, const Menu::arg *argv)
             interference_pct = motor_compensation.length() / (float)COMPASS_MAGFIELD_EXPECTED * 100.0f;
         }else{
             // interference is impact/amp * (max current seen / max throttle seen) / mag field * 100
-            interference_pct = motor_compensation.length() * (current_amps_max/throttle_pct_max) / 330.0f * 100.0f;
+            interference_pct = motor_compensation.length() * (current_amps_max/throttle_pct_max) / (float)COMPASS_MAGFIELD_EXPECTED * 100.0f;
         }
         cliSerial->printf_P(PSTR("\nInterference at full throttle is %d%% of mag field\n\n"),(int)interference_pct);
     }else{